Electron vortices in Atomic Ionization by a Single Few-Cycle Circularly Polarized Laser Pulse

Quantum vortices may occur not only in the wave functions but also in the amplitudes of various fragmentation processes, such as impact ionization$^{1-3}$. The structure of quantum vortices in the amplitude of the photodetachment by CP pulses was analyzed in the series of works$^{4-5}$, where the process was considered both, in multiphoton, and strong-field regime. Formation of electron vortices in the strong-field ionization was the subject of recent works$^{6-7}$. Here, the emergence of electron vortices in the ionization amplitude for an atom by an isolated few-cycle circularly polarized (CP) laser pulse is analyzed in the multiphoton regime within the perturbation theory (PT) framework. We demonstrate that the number of quantum vortices, vortex position and topological charge are determined by the relative magnitudes of the dynamical amplitude parameters corresponding to sequential photon absorption. By looking at the momentum distribution of the ionization amplitude phase, we show that these distributions exhibit spiral structures in the form of “Coulomb spirals”, which are signatures of the Coulomb scattering phases. We find that in region where the interference of dynamical variables of the ionization amplitude does not occur, the number of spiral arms correspond to the number of absorbed photons. In the region where the interference does occurs, the formation of an additional spiral arm is reported, which is due to quantum vortices being formed.

[1] J.M. Feagin, J. Phys. B \textbf{44}, 011001 (2010)

[2] J. H. Macek et al., Phys. Rev. Lett. \textbf{104}, 033201 (2010)

[3] J. S. Briggs and J. M. Feagin, Phys. Rev. A \textbf{90}, 052712 8 (2014).

4] L. Geng, F. Cajiao Velez, J. Z. Kaminski, L.-Y. Peng, and K. Krajewska, Phys. Rev. A \textbf{104}, 033111 (2021).

[5] L. Geng, F. Cajiao Velez, J. Z. Kaminski, L.-Y. Peng, and K. Krajewska, Phys. Rev. A \textbf{102}, 52 043117 (2020).

[6] O. I. Tolstikhin and T. Morishita, Phys. Rev. A 99, 063415 (2019).

[7] Y. Kang, E. Pisanty, M. Ciappina, M. Lewenstein, C. F. de Morisson Faria, and A. S. Maxwell, Eur. Phys. \textbf{59} J. D 75, 199 (2021).